Britain's most senior Catholic cleric has called on Christians to wear a cross every day as "a symbol of their beliefs" and to combat the marginalisation of religion in modern society.

The plea by Cardinal Keith O'Brien, head of the Catholic church in Scotland, to be made in his Easter sermon, comes as the Anglican archbishop of Canterbury, Dr Rowan Williams, appealed for more people to attend church this Sunday – even if they are "a bit vague" about religion.

Williams, who is marking his final Easter as leader of the Church of England, said he does not "lose sleep" over the fact many people only attend church at Easter and Christmas.

Speaking to BBC Radio 4, he said that he welcomed those with little connection to Christianity who just wanted to "let the story wash over them" knowing that they would not face a "doctrine examination".

But O'Brien will call on Christians to make the cross "more prominent in their lives". Due to speak at Edinburgh's St Mary's Cathedral on Sunday, he will tell them to "wear proudly a symbol of the cross of Christ on their garments each and every day of their lives".

He will say: "I know that many of you do wear such a cross of Christ, not in any ostentatious way, not in a way that might harm you at your work or recreation, but a simple indication that you value the role of Jesus Christ in the history of the world, that you are trying to live by Christ's standards in your own daily life."

His comments come as two women, who say they were discriminated against when their employers barred them from wearing the cross, are fighting to get their cases heard at the European court of human rights.

Nadia Eweida, 59, of Twickenham, south-west London, was suspended by British Airways for breaching the airline's uniform code in 2006. Shirley Chaplin, 56, from Exeter, was barred from working on wards by Royal Devon and Exeter NHS Trust after refusing to hide the cross she wore on a necklace chain.

O'Brien, the only British Catholic to be part of the college of cardinals – the Catholic church in England and Wales is headed by Archbishop Vincent Nichols – will quote Pope Benedict XVI, who said Christians "need to be free to act in accordance with their own principles".

He will say: "I hope that increasing numbers of Christians adopt the practice of wearing a cross in a simple and discreet way as a symbol of their beliefs.

"Easter provides the ideal time to remind ourselves of the centrality of the cross in our Christian faith.

"A simple lapel cross pin costs around £1. Since this is less than a chocolate Easter egg, I hope many people will consider giving some as gifts and wearing them with pride."

A Scottish government spokesman said: "Wearing a religious symbol is entirely a matter for individual members of staff. We have no policy as an employer."

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